"The Decline of Defined Benefit Retirement Plans and Asset Flows," by James
Poterba, Steven Venti, and David A. Wise (w12834, January 2007, .pdf format,
46p.).

Abstract:

Demographic change can have an important effect on the stock of assets held in
defined benefit pension plans. This paper projects the impact of changes in the
age structure of the U.S. population between 2005 and 2040 on the stock of
assets held by these plans. It projects the contributions to and withdrawals
from these plans. These projections are combined with estimates of the future
evolution of assets in 401(k)-like plans to describe the prospective impact of
demographic change on the stock of assets in retirement plans. Information on
demography-linked changes in asset demand is a critical input to evaluating the
potential impact of population aging on asset returns.